Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal; from feed stock intermediates, such as syngas; or from starchy materials or cellulose materials, such as corn and sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are often converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. In addition, water may be formed in an equal molar ratio with ethanol during the hydrogenation of acetic acid. These impurities limit the production and recovery of ethanol from such reaction mixtures. In addition, the impurities may be present in one or more purge streams. When impurities are present in water purge streams, the water purge stream must be treated, either chemically or biologically, to remove the impurities before the purge stream may be disposed. The further treatment adds costs and decreases the overall efficiency of producing ethanol.
Therefore, a need remains for an ethanol production process wherein the separation portion of the process produces a purified water stream that, as formed, contains little, if any, impurities. This water stream would not require further processing in order to be subsequently used or responsibly disposed.